This invention relates generally to printing equipment for encoding magnetic ink character recognition (MICR) characters on documents such as checks, commercial paper, and the like. More particularly, the invention relates to a high speed desk top MICR printing apparatus for use by bank tellers, point of purchase check-out register operators, bookkeeping departments, and the like, in recording magnetic ink character recognition symbols and characters in the predetermined fields along the bottom edge scan line or band reserved for MICR printing.
It is customary in the banking industry to encode checks, deposit slips and other commercial paper with machine readable magnetic ink charactes to facilitate the processing of financial transactions by machine. In order to insure compatibility throughout the banking industry, such machine readable information must be printed in conformance with very strict standards. If such standards are not adhered to the check or other document will not be machine processable and may have to be manually-handled--a very expensive and inefficient proposition.
In the case of checks, deposit slips and other financial transaction documents, a band along the lowermost edge of the document is reserved for MICR encoded information. The printing requirements for encoding MICR characters in this band are quite stringent and well documented in the literature. These stringent printing requirements are to some extent dictated by the sensitivity of the machines which read and sort MICR encoded documents. Also strict tolerances make falsification of financial documents more difficult. Generally speaking, when documents are rejected by the reader-sorter machine as being unreadable, some of the reasons for these rejects include: document size not meeting the standards for MICR sorting devices; density of ink too low or too high; MICR characters incorrectly positioned or spaced; presence of extraneous ink; symbols omitted; incorrect symbols used; inverted characters; other than MICR information printed in magnetic ink in the 1.59 cm (5/8 in.) reserved MICR band; presence of voids in characters; improper paper weight; and average edge tolerance not being acceptable for the reader-sorter.
Rejected documents must be taken out of the stream and sorted and entered by hand--a process estimated more than six times as expensive as automatic handling. Accordingly, printers for encoding MICR information on financial transaction documents must be capable of producing highly accurate and repeatable results. Printers heretofore available have achieved such accuracy and repeatability at the expense of printer speed.
The present invention provides a desk top MICR printing apparatus which will encode MICR information on the financial transaction documents well within the accuracy and repeatability tolerances required by the banking industry and at speeds not heretofore achieved by desk top units. In accordance with the invention the document printer comprises a print wheel rotatable about an axis having a plurality of raised characters disposed at predetermined angular positions about the periphery of the wheel. An electrically actuable print hammer is disposed radially of the print wheel and operates between retracted and print wheel impacting positions. A document transport mechanism supports the document along the bottom edge thereof and operates to transport or move the document in a direction parallel to the bottom edge, so that it passes between the print wheel and the print hammer. A print wheel stepper motor rotates the print wheel in incremental angular steps about the print wheel axis and includes a means for selectively positioning one of the raised characters in registration with the print hammer.
The print wheel stepper motor is driven by a motor driver which includes a means for determining which of the raised characters is in present registration with the print hammer and for further determining which of the raised characters is next to be printed. The motor driver further includes a means for determining the number of incremental angular steps needed to rotate the print wheel to a position where the next to be printed character is in registration with the print hammer. The motor drive means also includes a means for generating a plurality of current pulses for driving the print wheel stepper motor. The plurality of current pulses are generated at time intervals determined in accordance with the number of incremental angular steps needed to rotate the print wheel to its next printing position. The print wheel is stepped from its present or initial position to the next printing position at a rate which increases incrementally or accelerates from an initial rate or cold start rate to a maximum rate determined by the number of steps needed to rotate the wheel from its initial or present position to the next character to be printed position. As the print wheel nears the next character to the printed position, the driver incrementally decreases the step rate to decelerate the print wheel back towards the cold start rate. In this fashion, maximum speeds are achieved, accurately and without losing synchronism with the stepper motor.